The present invention relates to the continuous production of round copper wires, destined for electrical purposes, manufactured during the electrolytic refining of copper. Particularly the invention refers to a method and an apparatus to improve the present art of electrolytic copper refining, the elimination of the normal posterior process of rod manufacturing, the further avoidance of about sixty percent of the previously required reduction in the size of the rods by cold drawing to finish wires of smaller diameters and the heat treatment of the copper wires to impart the characteristics of electrical conductors.
The prior art produce of electrolytic copper refining are pure copper plates commonly named "cathodes" which are about 3.3 ft (1000 mm) square and about 5/8 inch (15 mm) thick and are formed by electrodeposition of pure copper on starting sheets (thin leaves of refined copper). These leaves, also measuring about 3.3 ft square but about 0.04 inch (1 mm) thick, have to be intermittently introduced into the electrolytic tanks as the engrossed refined cathodic plates are removed as finished product, both operations using manual work. The electrolysis is carried out at low current densities (the amperage applied to the tanks spread over the immersed surfaces of the total number of the cathodic starting sheets present, or expressed in terms of the wetted areas of the crude copper anodes being refined) as otherwise the electricity required and thus the power cost, increases governed by Ohm's law directly proportional to the increase in current density. Under present economic factors current densities (cathodic or anodic) of (about 20 to 40 amp/ft.sup.2 about 200 to 400 amp/m.sup.2) are successfully used, resulting in a tankhouse consumption of about 230 kilowatt-hours of electricity per metric ton of cathodes produced and considering other accessory equipment, an overall refinery requirement of about 330 kw-hr per metric ton of copper is normal practice.
In order to use the prior art refined cathode plates to manufacture electric wires, such cathodes have to be melt, cast and hot rolled in a separate and complex facility in order to produce round rods; a process which additionally consumes about 350 kilowatt-hours of energy per metric ton of rod and involves considerable labor. Such rods are normally 5/16 inch (7.94 mm) in diameter. Furthermore, to convert these rods to round copper wires an additional facility is normally needed for cold drawing or "rod breakdown" as well as for annealing, consuming additionally about 70 kw-hr of power per metric ton of finished wire such as AWG 4 in size (5.189 mm diameter).
Thus, it is recited that the prior art of copper wire production destined for electrical purposes, starting with an electrolytic refining process, consumes a total of about 750 kw-hrs of energy per metric ton of produced wire 0.2043 inch (5.189 mm) in diameter.
U.S. Pat. No. 4,196,059 discloses a method and an apparatus for continuously introducing a thin copper wire as cathodic starting or base surface into a complicated tank for refining impure copper anode blocks thereby engrossing said wire by electrolytic deposition to a large diameter rod (about 20 mm) which constitutes its finished product. Excellent novelties are claimed to be able to operate at high current densities while preventing the contamination of the refined rod by the normal impurities found in the anode slime residues. But despite its merits for particular applications it is not suitable for production of electric wires directly by electrolysis because its large consumption of energy would defeat the purpose of improving the present art. Said apparatus consumes about 1200 kw-hrs of electricity per metric ton of produced rod as a result of the relatively large voltage necessary to operate at about 93 amp/ft.sup.2 (1000 amps per square meter) plus the significant voltage drop in its baskets of high electrical resistance used to hold the anodes and in the necessary membranes barrying contaminants. Furthermore, the later processing (drawing and annealing) of a 20 mm copper rod to electric wire such as AWG 4 would require about 190 kw-hr of energy per metric ton, resulting in a total consumption of energy by said disclosure of about 1400 kw-hr/metric ton of wire, as compared to about 750 kw-hr per ton by actual conventional techniques.
Additionally the disclosure apparatus has inherent impediments to refine customary sized impure copper anodes at normal current densities. Firstly, said apparatus feeds each wire base or starting wire from an individual drum or reel and as 50 to 100 starting wires are necessary per anode row in order to obtain a large enough cathodic surface to spread the applied amperage over a sufficient area, the same large number of pay-off stations would be necessary but the physical dimensions of a tank prevent their appropriate location. Secondly, the struts used by said apparatus to support the starting wires in the tank and the wiper contacts to the negative terminal of the current supply require a substantial vertical dimension which impossibilitates placing the wires close enough to each other so as to achieve the proper cathodic surface area.
U.S. Pat. No. 4,395,320 also discloses an apparatus working on electroplating principles to engross wires but again its merits are in the opposite direction of the present invention. The apparatus thereby described consists of a cascade of electrolytic baths separated by rollers pressing on the wire being engrossed in order to smooth its rough surface consequent to the very high current densities objectively utilized. Such an apparatus, complicated with said rotatable rollers operating at current densities of about 280 amp/ft.sup.2 (30 amp/dm.sup.2) demands more than 2000 kw-hrs of electricity per metric ton of copper wire produced, also considering the energy lost by the high electrical resistivity of the anode baskets employed. Therefore its application to improve present copper refining by the elimination of the cumbersome normal flat starting sheets and attain the objective to avoid the customary rod making stage are precluded by its prohibitive energy consumption. Furthermore, the baskets used by said disclosure to hold the anodic crude copper, in relatively small granules, impossibilitates refining normal impure anodes measuring about 1000 mm square, 45 mm thick and weighing each about 350 kg. Additionally, the high rate ofelectrolytic circulation required by said apparatus to operate properly would considerably disturb the free settling of the anodic residue slimes to the bottom of the electrolytic tank and flowing proximate to the pure cathodic wire the impurities contained in such residues would co-deposit, debasing the refined product.
Therefore, as U.S. Pat. Nos. 4,196,059 and 4,395,320 were envisioned for other particular purposes they are incapable to improve the current practice of electrical wire manufacturing. Such practice starting with electrolytic refining of copper that engrosses thin starting sheets to large "cathodes" which have to be melt, cast and rolled to rod and the rods further drawn down to wire sizes thus continues as the generalized art.